1. Field
The present disclosure relates to the design of face seals (FS) for filtering facemask respirators (FFR), and specifically to minimizing FS inward leakage (FSIL) that occurs in FFRs.
The present disclosure also relates to the use of heat activated thermoplastic copolymers in the construction of a FS, and to critical areas of the human facial anatomy as they relate to FSIL.
2. Description of the Related Technology
Filtering face piece respirators (FFRs) play a critical role in everyday life. They are available for purchase to the general public in most hardware stores and are recommended, or required, for use in a wide variety of home, public, and occupational environments—especially in healthcare settings. Their principle function is to provide respiratory protection against both non-biological and biological particulate materials.
In practice, FFRs are used generally to protect the wearer. In healthcare institutions, and public health settings, however, FFRs must function both to protect the wearer from potentially harmful particulate matter, including biological pathogens, and/or to protect populations from a wearer exhaling such pathogens into the environment. During surgical procedures, for example, the smoke plume generated from electrosurgical use has been shown to contain a wide variety of vaporized viral organisms capable of infection, including HIV and Human Papilloma Virus (HPV). A FFR in such a setting must therefore protect the surgeon and those in the operating room, while at the same time protecting the patient from the surgeon's exhaled pathogens coming into contact with the surgical field. In certain public health settings, FFRs must be able to effectively protect the wearer and/or the surrounding human contacts from biological organisms in a wide range of sizes: from large bacteria at 0.300 to 1.0 micros, to the H7N7 and H7N9 Asian flu virion, where the particle size can be as small as 40-80 nanometers.
The design features of any FFR that provide its intended protection to the user are: 1) the filter element itself, and 2) the mechanism of sealing the mask to the wearer's face.
With respect to the filter materials in the FFR assembly: FFRs are certified by the National Institutes of Occupational Safety and Health's (NIOSH) approval regulation 42 CFR 84, to provide a variety of levels of protection. These NIOSH ratings range from having 95% efficiency at filtering non-oil based aerosolized particulate matter (N95), to 100% efficiency (P100) in filtering particulate matter that is oil-based where the filter itself must be strongly resistant to oil. Volatile organic compounds (VOCs) and other such vapor hazards require half face or full face elastomeric respirators with specific cartridge-based filters (OV/P100), which are commonly referred to as “gas masks”.
At the other extreme are simple so-called “dust masks”, and surgical masks. It should be noted that surgical masks are not FFRs and are not certified for use by the NIOSH. Likewise, so-called “N95 surgical mask respirators”, while being NIOSH certified with respect to the “N95” rating, are not certified by the NIOSH for use in surgery. Instead, a surgical mask of any kind must pass the FDA's approval process which uses testing standards of the American Society of Testing and Materials (ASTM): F1862, F2100-11, and F2101-07.
For the FFR to provide the stated protection level to the user, it must pass the Occupational Safety and Health Administration's (OSHA) respirator standard 29 CFR 1910.134, Appendix A, Part 1: “Accepted Fit Test Protocols”, Section A: “Fit Testing Procedures—General Requirements”, pp. 1-13, which involves an initial “user seal test” to evaluation the FFR for obvious leaks around the edges of the mask.
A second, more specific fit testing may then be required: OSHA 29 CFR 1910.134, Appendix A, Part 1: “Accepted Fit Test Protocols”, Section A: “Fit Testing Procedures—General Requirements”, pp. 14A: “Test Exercises”, subsec 1-8 and pp 14B. This is performed with optical particle counters, and looks specifically at the actual particle concentrations outside and inside the mask while it is being worn. In essence, this is a test of how well the FS on the FFR performs in relationship to the filter rating of the FFR. This difference, depending on the experimental design and the filter rating, can represent the FFR's FSIL.
With respect to sealing the mask to the wearer's face, the principal reason to achieve such a seal is to avoid leakage around, rather than through, the filter portion of the mask. This is true for both inhaled and/or exhaled particulate matter coming from the user. There are two components involved: the straps that hold the mask to the face, and the FS itself.
NIOSH certification of FFRs has been a major advance in the development and classification of effective filters for FFRs. However there remains a significant problem with FSIL between the mask and the user's face. FSIL has been shown to occur in virtually all N95 FFRs and is dependent on multiple factors including: overall design of the FFR; FS design and the material used; the mechanism of attachment of the FFR to the wearer's face; and the particle sizes being filtered. Most reports conclude that the overwhelming factor in FFR FSIL is the FS component itself. That is, the filter elements themselves perform very well, if not exceeding the NIOSH certification standards. Yet if there is any degree of FS failure, the protection factor (PF) of the FFR can drop significantly: the reduction of protection due to FSIL in some N95 FFRs has been shown to be up to a 90% failure to filter out sub-micron size aerosolized particles. This is true for particle sizes less than 0.300 μm, which includes many viruses in the size ranges of 40-120 nanometers, in particular the Swine flu and Avian flu viruses.
FSIL creates a unique problem for healthcare workers in operating room settings on two fronts:
The first is that a smoke plume is generated during the customary widespread use of electrocautery during surgical procedures. OSHA estimates that 500,000 workers are exposed to laser and electrocautery smoke each year. Electrocautery creates particles with the smallest mean aerodynamic size of 0.07 μm—far smaller than the filtering capability of a N95 FFR. Studies have shown that a range of aerosolized toxins are present, including multiple volatile organic compounds that are either known, or suspected, carcinogens. Intact strands of human papillomavirus DNA have been isolated from carbon dioxide laser plumes during treatment of plantar warts and recurrent respiratory papillomatosis. Viable bacteriophage have also been demonstrated to be present in laser plumes. Whole intact virions have been found and their infectivity demonstrated. HIV DNA has been identified in laser smoke, and has also been shown to be capable of transmitting infections into cultured cells.
As far back as 1981 there were opinions being stated as to the need for new standards for protective masks in the operating room environment (see: “Proposed Recommended Practice for OR Wearing Apparel, AORN JOURNAL, v. 33, n. 1, pp. 100-104, 101. 1981”). The AORN has also published a Position Paper on the hazards of surgical smoke for several years, calling for “ . . . high filtration surgical masks (to be) worn properly”.
It is recognized that the inhalation dangers in surgical settings are compounded by the non-use of N95 respirators in all but those procedures involving HPV containing lesions—such as in the laser removal of genital warts. In the vast majority of surgical procedures, during which extremely high levels of particulate material are generated into the smoke plume, there is no requirement for N95 FFRs to be worn. Many investigators now agree that the protection provided by surgical masks may be insufficient in environments containing potentially hazardous sub-micron-sized aerosols.
However, even if N95 FFRs were to be required in operating rooms to protect the user from the wide range of harmful particles in surgical smoke, the FSIL failures of such FFRs will result in significant reductions of the expected protection afforded to the user.
The second problem unique to the operating environment is the shedding of potentially infectious bacteria onto the surgical field. A vast majority of surgical masks in use today are of a comparatively loose fitting nature and do not generally have a tightly sealed facial border. Typically such masks are manufactured from a variety of molded layered fibrous filtration materials designed for one-time disposable usage. U.S. Pat. No. 3,613,678 (Mayhew), U.S. Pat. No. 5,307,796 (Kronzer), U.S. Pat. No. 4,807,619 (Dyrud) and U.S. Pat. No. 4,536,440 (Berg) are all examples of the prior art. These features of surgical masks have raised concerns about the limitations of surgical masks, dating as far back as 1941, and continuing to the present day as to the effectiveness of such masks in preventing infections in surgical patients. Studies have confirmed that passage of inspired air around the periphery of two types of face masks appears to circumvent the mask's ability to screen airborne contaminants. Similar studies have revealed that Gram-positive staphylococci bacteria—a highly common cause of surgical site infections (SSI), were frequently isolated from air samples obtained throughout the operating room, including areas adjacent to the operative field. Nasopharyngeal shedding from persons participating in the operation was identified as the source of many of these airborne contaminants. Failure of the traditional surgical mask to prevent microbial shedding is likely associated with an increased risk of perioperative contamination. These deficiencies take on considerable importance with respect to the costs, both physical and economic, of surgical site SSIs. A 2009 high profile report by the CDC's Division of Healthcare Quality Promotion estimated that there were 290,485 SSI's per year in US hospitals—16% of all hospital acquired infections, second only to urinary catheter related infections. With an estimated average cost of $17,500 per patient, these SSI's cost upwards of $22 million dollars per year.
Given the previously discussed FSIL issues with all FFRs, in relation to the sizes of inhaled pathogens, and the sizes of exhaled pathogens, it is accurate to conclude that even the addition of N95 surgical mask respirators in the operating room will be unlikely to have a significant impact on the shedding of potentially harmful organisms from exhalations vapors of surgical personnel into the surgical field.
There have been many ongoing efforts by those of skill in the art to address the well-documented issue of FSIL in FFRs, and in surgical masks. The most basic design feature used to achieve some degree of a tight fit to the wearer's face has been to design the mask body, both in surgical masks and in FFRs, to be generally cup-shaped, and to have some form of a shaping layer where the inner mask perimeter has some slight curvature of the region from the nasal bridge itself down on to the sides of the nose. Simple face masks, including surgical face masks, as well as FFRs have utilized this design concept extensively. U.S. Pat. No. 3,613,678 (Mayhew), U.S. Pat. No. 5,307,796 (Kronzer), U.S. Pat. No. 4,807,619 (Dyrud), U.S. Pat. No. 4,536,440 (Berg), U.S. Pat. No. 4,873,972 (Magidson), U.S. Pat. No. 4,827,924 A5 (Japuntich), and U.S. Pat. No. 6,923,182 (Angadjivand) are just a few such examples that are well known to those reasonably skilled in the prior art.
Another very common design, in an effort to improve the FS at the nasal bridge section, is to include a malleable nose clip or bar that is secured on the outer face of the mask body centrally adjacent to its upper edge to enable the mask to be deformed or shaped in this region in order to obtain a better fit along what is commonly referred to as the “bridge” of the nose. Such nose bars, or clips, are well known to those reasonably skilled in the prior art.
A nose clip is described in U.S. Pat. No. 5,558,089 (Castiglione), Pat. App, 2011/0067700 (Spoo) and U.S. Pat. No. 5,307,796 (Kronzer). These are just a few such examples of the prior art.
Such nose clips are also commonly associated with a strip of foam affixed to the length of the clip, typically made from materials of either polystyrene, polyester, or neoprene. Examples of such foam strips are described in U.S. Pat. No. 5,765,556 (Brunson), and U.S. Pat. App. 2005/0211251 (Henderson).
Another design feature on FSs of the prior art, to improve the FS fit at the nasal bridge section, is to add some varying degree of asymmetric outward extension to make the foam strip wider at the sides of the nasal bridge. One such example is U.S. Pat. No. 8,171,933 (Xue) which describes a preformed nose clip that follows a general curve off the nasal bridge to the sides, exerting a force resiliently inward on each side of the wearer's nose when the mask is worn. This feature is claimed to eliminate the need for the wearer to individually shape the nose clip to the wearer's face. Another such example is U.S. Pat. 2008/0023006 (Kalatoor) which also describes a mask body where at least the first major surface of the nose foam has a predetermined concave curvature, which is claimed to have less opportunity to become pinched or unnecessarily deformed before being placed on wearer's face. These examples differ substantially from the present disclosure in that: the foam strip in these examples only involves the nasal portion of the FS perimeter; it has no inward convex protrusions to address the rest of the entire FS perimeter; and in that it does not involve any specific anatomically defined inner perimeter convex accentuations of the FS that conform specifically to the critical fit zones (CFZs) of the human face as described herein, and as will be further described in the illustrations below of the present disclosure.
Another such example is U.S. Pat. App. 2008/0099022 (Gebrewold), which describes a respiratory mask that has a nose foam that has a particular preconfigured shape for assisting in providing a snug fit over the wearer's nose. The nose foam has a nose-contacting surface that is skewed at first and second angles to a plane that extends to the nose foam. It is also claimed that the fit may be able to be achieved without use of a nose clip. However, this device differs substantially from the present disclosure in that the design feature described does not address the entire 360 degrees of the FS perimeter, and in that it does not involve any other specific anatomically defined inner perimeter convex accentuations of the FS that conform specifically to the CFZs of the human face as described herein, and as further described in the illustrations below of the present disclosure.
Another design feature to improve the FS fit is to include a vapor seal either across the top portion of the mask to assist in preventing fogging of the mask, or around the entire perimeter of the mask. U.S. Pat. No. 5,383,438 (Raines) is an example of such a design feature, as is U.S. Pat. No. 5,553,608 (Reese), which describes a stretchable material around the mask. Such a feature is well known to those reasonably skilled in the prior art. These features differ substantially from the present disclosure in that the FS design in these examples has no specific anatomically defined inner perimeter convex accentuations that conform specifically to the CFZs of the human face as described herein, and as further described in the illustrations below of the present disclosure.
Another design feature of face masks and FFRs of the prior art, in order to improve the FS fit to the user's face, is to utilize different materials than other such masks of the prior art. One such example is U.S. Pat. App. 2007/0039620 (Sustello), which uses an expandable or compressible material, such as a viscoelastic foam, or other such materials with similar characteristics, to enhance a seal between the mask and a user's face in an area extending over the bridge of the nose and generally under the eyes. However this represents a thin layer of viscoelastic material across the nasal section only, and is primarily intended to minimize fogging of a user's glasses or goggles due to warm humid exhalation vapors that, in fact, escape the FS due to FSIL in the device itself. Unlike the present disclosure, the feature described also doesn't involve any specific anatomically defined inner perimeter convex accentuations that conform specifically to the CFZs of the human face as described herein, and as further described in the illustrations below of the present disclosure.
Another example is U.S. Pat. App, 2012/0017911 (Choi), which describes a mask housing that is made entirely of a closed cell foam layer that has a plurality of fluid permeable openings located therein. The closed cell foam shaping layer is claimed to provide a sufficient degree of pliability at the perimeter, and is also claimed to enable the mask body to fit comfortably and snugly on a wearer's face without attachment or use of an elastomeric face seal, nose foam, or nose clip. However, unlike the present disclosure, this device does not involve any specific anatomically defined inner perimeter convex accentuations of the FS that conform specifically to the CFZs of the human face as described herein, and as further described in the illustrations below of the present disclosure.
Some existing FFRs use some form of an adhesive to attach the face seal directly to the user's face. U.S. Pat. No. 6,125,849 (Williams) is one such example. Another such example is U.S. Pat. No. 8,381,727 (Matich), which describes a mask with a FS comprised of an endless skin adhesive seal on the inside of the covering, with multiple such adhesive seals applied to each other and the inside of the mask shell perimeter. The authors provide examples of fit factors (FFs) determined by scientific measuring protocols and methods that are well to known to those reasonably skilled in the prior art. The results showed overall FF improvements of 20-80 percent when the seal was applied to industry standard N95 FFRs, versus the same FFRs with their stock FSs. Some individual FFs were over 300 in “experienced users”, and as high as 1170. However, the use of N95 FFRs for such experimental studies can be considered problematic. This is due to the fact that for a given N95 FFR, a 5% total IL can be expected. Thus if one is trying to compare two FSs for only their FSIL component of the total IL on a given N95 FFR, then the IL measured cannot entirely be distinguished as only FSIL versus trans-filter leakage through the N95 FFR's filter element.
There have also been concerns about comfort issues with adhesives, applied directly to the face, being removed on a regular basis as would be required in many healthcare settings, particularly in surgical settings.
FSIL is difficult to reduce because of the significant variances in human facial anatomy. Anthropometric studies have revealed the substantial differences in the multiple variables of human facial anatomy. These are notable, perhaps not coincidentally, in the three areas that are common for FSILs to occur: 1) the nasal bridge and the cheek bone, 2) the cheek bone to the edge of the lower jaw, and 3) around and under the area between the undersurface of the chin back toward the angle of the jaw. The problem of FSIL may also be compounded by FFRs being made in fairly generic “small, medium, and large” sizes, and often simply as a “one size fits all” design. Therefore it can be seen that for existing FFRs:                That FSIL is a major problem that impairs critical protection by up 90%        That FSIL is due almost completely to failure of the FS itself        That FSIL occurs in specific areas where a FS contacts the human face        That multiple studies by multiple individuals and institutions of skill in the art have shown that existing FS designs do not compensate for all such known anatomic areas that correspond to such areas of FSIL.        
There is therefore a need to redesign FFR FSs to decrease, or even eliminate FSIL. The present disclosure achieves this, by addressing all of the above factors, and represents an entirely new concept in FS design. The present disclosure's design is based on:                specifically defined CFZs identified in human facial anatomy that correspond to the known areas of FSIL        the specific compensations for these areas in the geometric design of the FS that correspond to the CFZs involved in FSIL        the thermally-activated heat-fitting characteristic of the material used in the FS, such that the FS can be actively fitted to the user's face        
Testing results at the laboratory level, and confirmed in studies of both Simulated Workplace Protective Factor (SWPF) and Work Place Protective Factor (WPF) settings, performed with N100 FFRs to eliminate the filter element itself as a factor in FSIL, have shown that the level of FSIL reduction provided by this presently disclosed apparatus represents a highly significant improvement in FS and FFR technology. The protection factors measured are 60-240 times higher than FFR FSs of the prior art, and the geometric means (GMs) of the WPFs were over 21,000.